fix(processing): guard completionPromise as write-once (singleton promise)

Prevent concurrent safeComplete* calls from overwriting completionPromise
with a no-op. The guard now lives at the assignment site — if a completion
is already in-flight, return its promise instead of starting a new one.
This ensures waitForCompletion() always awaits the real work.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: waleedlatif1

apps/sim/lib/logs/execution/logging-session.ts

@@ -689,6 +689,7 @@ export class LoggingSession {
   }
 
   async safeComplete(params: SessionCompleteParams = {}): Promise<void> {
+    if (this.completionPromise) return this.completionPromise
     this.completionPromise = this._safeCompleteImpl(params)
     return this.completionPromise
   }
@@ -713,6 +714,7 @@ export class LoggingSession {
   }
 
   async safeCompleteWithError(params?: SessionErrorCompleteParams): Promise<void> {
+    if (this.completionPromise) return this.completionPromise
     this.completionPromise = this._safeCompleteWithErrorImpl(params)
     return this.completionPromise
   }
@@ -739,6 +741,7 @@ export class LoggingSession {
   }
 
   async safeCompleteWithCancellation(params?: SessionCancelledParams): Promise<void> {
+    if (this.completionPromise) return this.completionPromise
     this.completionPromise = this._safeCompleteWithCancellationImpl(params)
     return this.completionPromise
   }
@@ -764,6 +767,7 @@ export class LoggingSession {
   }
 
   async safeCompleteWithPause(params?: SessionPausedParams): Promise<void> {
+    if (this.completionPromise) return this.completionPromise
     this.completionPromise = this._safeCompleteWithPauseImpl(params)
     return this.completionPromise
   }